Electrostatic coating machine

Abstract

An electrostatic coating machine according to the present embodiments can reduce the risk of sparking even when setting a higher line speed than before when performing coating according to a proximity painting method. In the coating machine that performs electrostatic coating by use of a high voltage generated by a cascade, when a time constant τ is defined as the product of a total capacitance Co of the electrostatic coating machine and a bleeder resistor R 1 , the product of the total capacitance Co and the bleeder resistor R 1 is set so that the time constant τ is 0.005 to 0.050.

We claim: 
     
         1 . An electrostatic coating machine configured to perform electrostatic coating by charging the coating with a voltage generated by a cascade and directing the coating toward a grounded workpiece, wherein the cascade comprises
 a resistance to ground;   a capacitance to ground, wherein the resistance to ground and capacitance to ground are in parallel; and   a time constant, wherein the time constant is an arithmetic product of the resistance to ground in ohms and capacitance to ground in farads, wherein the time constant is between 0.005 seconds and 0.050 seconds.   
     
     
         2 . The electrostatic coating machine of  claim 1 , wherein the time constant is between 0.015 seconds and 0.033 seconds. 
     
     
         3 . The electrostatic coating machine of  claim 2 , wherein the time constant is between 0.018 seconds and 0.030 seconds. 
     
     
         4 . The electrostatic coating machine of  claim 1 , wherein the resistance to ground comprises a bleeder resistor in parallel with a direct current power supply, wherein the bleeder resistor comprises a first bleeder resistor connection between a terminal of the direct current power supply and a second bleeder resistor connection to ground. 
     
     
         5 . The electrostatic coating machine of  claim 4 , wherein the bleeder resistor comprises a resistance of 1000 megaohms to 2000 megaohms. 
     
     
         6 . The electrostatic coating machine of  claim 4 , wherein the capacitance to ground consists of a first capacitance and a second capacitance, wherein the first capacitance comprises primary first capacitance connection between a terminal of the direct current power supply and a secondary first capacitance connection to ground. 
     
     
         7 . The electrostatic coating machine of  claim 6 , wherein the capacitance to ground is between 20 and 40 picofarads, and the value of the first capacitance is the capacitance to ground minus a second capacitance. 
     
     
         8 . The electrostatic coating machine of  claim 7 , wherein the second capacitance comprises a primary second capacitance connection between a series resistor and an applicator and a secondary second capacitance connection to ground. 
     
     
         9 . The electrostatic coating machine of  claim 8 , wherein the second capacitance is in parallel with the bleeder resistor and the first capacitance. 
     
     
         10 . The electrostatic coating machine of  claim 1 , further comprising an output voltage control unit configured to reduce the absolute value of the voltage generated by the cascade without stopping the output of the high voltage generator when the output current reaches a current limit value. 
     
     
         11 . The electrostatic coating machine of  claim 10 , wherein the current limit value is a dynamic value based on the voltage generated by the cascade. 
     
     
         12 . The electrostatic coating machine of  claim 11 , wherein the current limit value increases as the absolute value of the voltage increases within a first voltage domain. 
     
     
         13 . The electrostatic coating machine of  claim 12 , wherein the current limit value is static as the absolute value of the voltage increases within a second voltage domain, wherein the second voltage domain is higher than the first voltage domain. 
     
     
         14 . The electrostatic coating machine of  claim 13 , wherein the output voltage control unit is configured to stop voltage generation by the cascade when the output current reaches an absolute sensitivity value, wherein the absolute sensitivity value is a dynamic value based on the voltage generated by the cascade. 
     
     
         15 . The electrostatic coating machine of  claim 14 , wherein the absolute sensitivity value increases as the absolute value of the voltage increases within the first voltage domain, and wherein the absolute sensitivity value is static as the absolute value of the voltage increases within the second voltage domain.